4 MASS. EXPERIMENT STATION BULLETIN 380 



to the parent material from which the soil was derived. Perhaps at this point 

 it would be well to distinguish between the formation of soil material chiefly 

 through geological processes of weathering, and the differentiation of this material 

 into layers or horizons through the processes of profile development. According 

 to Professor G. VV. Robinson: 



We must regard weathering, physical and chemical, as essentially a 

 geological process, fulfilled, it is true, in the superficial layers of the earth's 

 crust in close relationship with the soil and its processes. The develop- 

 ment of the soil profile must be regarded as superimposed on the geological 

 process of rock weathering. ^ 



The importance of a careful consideration of the soil profile is shown by the 

 following quotation, also from Robinson: 



The soil profile is the significant factor in the study of relationship of 

 the soil to plants, not only because the profile embraces the root system of 

 plants growing on the soil but also because the all-important factors, 

 moisture and air, can be defined only in terms of the soil profile and not 

 in terms of the laboratory samples. It is important also because a study 

 of its characters can give information as to its probable behavior under 

 different types of management and as to its suitability for different crops. 

 In the soil profile we can read the past history of the soil and forecast its 

 future possibilities.2 



Although the major characteristics of fully developed soil profiles under virgin 

 conditions are largely determined by climatic forces; in regions like Massachusetts, 

 where the soils are young and their profiles immature, other factors such as the 

 nature of the parent geological material exert strong modifying influences. With 

 soils long farmed, pronounced alterations from virgin conditions have been 

 brought about as a result of tillage, cropping, and fertilizer practices. Therefore, 

 to fully understand the nature of Massachusetts soils and to comprehend their 

 limitations and potentialities, the modifications resulting from human interven- 

 tion must be carefully considered in conjunction with the effects of climatic and 

 geological factors. 



The Influence of Geology 



Since geological factors determine the nature of the parent soil material, it 

 seems advisable to indicate briefly the geological background of the present land 

 topography of Massachusetts. Leading up to this present topography is a 

 long history replete with a great variety of geological activity. From the earliest 

 era of the geological time scale, long periods of deposition have alternated with 

 long periods of profound erosion. At times uplifting processes were so violent 

 that lofty mountain systems were raised, accompanied by much tilting and fold- 

 ing and subsequent faulting of rock strata. Volcanic action has also occurred 

 intermittently, whereby great quantities of molten igneous material were forced 

 up into the sedimentary strata and occasionally appeared as lava outpourings 

 on the surface. These mountain systems have been largely worn away so that 

 the present land surface of Massachusetts exemplifies well the descriptive termi- 

 nology often given the New England area — "a worn -down mountain region." 

 The removal of vast quantities of material through prolonged erosive action has 

 exposed a great variety of rocks of different ages and of different physical and 

 chemical characteristics. The great diversity in the nature of the parent rock 

 material from which our soils have been developed has been one factor, though 

 not the most important, in the formation of the many varied types of soils which 

 are now found in the State. 



'Mother Earth — Letters on Soil (London, 1937). p. 63. 

 2lbid., p. 14. 



